Adaptive isogeometric analysis by local h-refinement with T-splines

Isogeometric analysis based on non-uniform rational B-splines (NURBS) as basis functions preserves the exact geometry but suffers from the drawback of a rectangular grid of control points in the parameter space, which renders a purely local refinement impossible. This paper demonstrates how this difficulty can be overcome by using T-splines instead. T-splines allow the introduction of so-called T-junctions, which are related to hanging nodes in the standard FEM. Obeying a few straightforward rules, rectangular patches in the parameter space of the T-splines can be subdivided and thus a local refinement becomes feasible while still preserving the exact geometry. Furthermore, it is shown how state-of-the-art a posteriori error estimation techniques can be combined with refinement by T-splines. Numerical examples underline the potential of isogeometric analysis with T-splines and give hints for further developments.     

Stabilization of foams and emulsions by mixtures of surface active food-grade particles and proteins

Surface active biopolymers such as proteins can form films with particularly high interfacial elasticities and viscosities and these molecules are widely exploited as foaming and emulsifying agents in foods. Solid particles of the correct size and wetting characteristics can also be extremely effective stabilizers of foams and emulsions, although the underlying mechanism of stabilization is somewhat different. Relatively little is known about what happens when both surface active polymers and surface active particles are present together. This work presents recent findings on the effects of mixtures of proteins plus novel food-compatible surface active particles. The proteins include caseins and whey proteins. The surface active particles prepared include cellulose + ethyl cellulose complexes, hydrophobically-modified starch granule particles and stable (non-spreading) protein-stabilized oil droplets. Interfacial shear rheology of adsorbed films was measured via a biconical bob apparatus and interfacial dilatational rheology was measured via a Langmuir trough type apparatus. The corresponding stability of bubbles to coalescence and disproportionation was assessed in separate experiments. Stability of oil-in-water emulsions was assessed via measurement of particle size distributions as function of time and visual assessment of the tendency to creaming and oiling off. In general, it is shown that the surface active particles on their own exhibit much lower measures of interfacial elasticity and viscosity than the proteins, but in combination with the proteins they appear to enhance the interfacial viscoelasticity considerably, with concomitant increases in bubble and emulsion droplet stability. There is little evidence of attractive interactions between the particles and the proteins, so a possible explanation of the increased stability is that the proteins increase the accumulation of particles at the interface, giving rise to increased jamming of particles at the interface.     

Label Transfer Reagents to Probe p38 MAPK Binding Partners

Protein kinases are essential enzymes for cellular signaling, and are often regulated by participation in protein complexes. The mitogen‐activated protein kinase (MAPK) p38 is involved in multiple pathways, and its regulation depends on its interactions with other signaling proteins. However, the identification of p38‐interacting proteins is challenging. For this reason, we have developed label transfer reagents (LTRs) that allow labeling of p38 signaling complexes. These LTRs leverage the potency and selectivity of known p38 inhibitors to place a photo‐crosslinker and tag in the vicinity of p38 and its binding partners. Upon UV irradiation, proteins that are in close proximity to p38 are covalently crosslinked, and labeled proteins are detected and/or purified with an orthogonal chemical handle. Here we demonstrate that p38‐selective LTRs selectively label a diversity of p38 binding partners, including substrates, activators, and inactivators. Furthermore, these LTRs can be used in immunoprecipitations to provide low‐resolution structural information on p38‐containing complexes.     

Combustion synthesis of ultra-fine SiC powders in low pressure N2-atmosphere

Ultra fine SiC nano-powders (100–300 nm) of high purity were successfully produced by combustion of a powder mixture of Si and C, with the addition of poly-tetra-fluoro-ethylene (PTFE) as a chemical stimulator, in a moderately pressurized nitrogen atmosphere (1–10 MPa). The experimental results showed that with the aid of mechanical activation of the starting powders, a small amount of PTFE (1.5 wt%) can effectively stimulate the reaction between Si and C. Both the experimental results and thermodynamic calculations indicate that the formation of Si₃N₄ plays a key role in the process. The optimum conditions for producing the aforementioned SiC fine powders were 1.5 wt% PTFE, 1 MPa N₂ pressure and no addition of diluents of SiC powder.     

Highly stable hydrophobic SiNCO nanoparticle‐modified silicon nitride membrane for zero‐discharge water desalination

Membrane distillation water desalination can attain a significantly higher water recovery than reverse osmosis, while the lack of stable hydrophobic membranes limits its commercial applications. This article presents the preparation of a new hydrophobic membrane by modifying a porous Si₃N₄ substrate with vesicular SiNCO nano‐particles. The membrane had a water contact angle of 142°, due to the presence of –Si–CH₃ terminal groups and the high surface roughness. The contact angle remained nearly the same after exposures of the membrane to boiling water, aqueous solutions with pH ranging from 2 to 12, and benzene. The membrane exhibited satisfactory water desalination performance on highly concentrated NaCl solutions and simulated seawater. With the highly stable membrane, it is promising to develop a zero‐discharge water desalination process for simultaneous production of fresh water for daily uses and brine for industrial uses. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1272–1277, 2017     

The development and experimental validation of a reduced ternary kinetic mechanism for the auto-ignition at HCCI conditions,proposing a global reaction path for ternary gasoline surrogates

To acquire a high amount of information of the behaviour of the Homogeneous Charge Compression Ignition (HCCI) auto-ignition process, a reduced surrogate mechanism has been composed out of reduced n-heptane, iso-octane and toluene mechanisms, containing 62 reactions and 49 species. This mechanism has been validated numerically in a 0D HCCI engine code against more detailed mechanisms (inlet temperature varying from 290 to 500 K, the equivalence ratio from 0.2 to 0.7 and the compression ratio from 8 to 18) and experimentally against experimental shock tube and rapid compression machine data from the literature at pressures between 9 and 55 bar and temperatures between 700 and 1400 K for several fuels: the pure compounds n-heptane, iso-octane and toluene as well as binary and ternary mixtures of these compounds. For this validation, stoichiometric mixtures and mixtures with an equivalence ratio of 0.5 are used. The experimental validation is extended by comparing the surrogate mechanism to experimental data from an HCCI engine. A global reaction pathway is proposed for the auto-ignition of a surrogate gasoline, using the surrogate mechanism, in order to show the interactions that the three compounds can have with one another during the auto-ignition of a ternary mixture.     

Bacteriological quality of “doubles” sold by street vendors in Trinidad and the attitudes, knowledge and perceptions of the public about its consumption and health risk

The bacteriological loads of “bara”, “channa”, condiments/spices and ready-to-consume “doubles” sold by street vendors in St. George and Caroni counties of Trinidad were determined. Questionnaires were administered to 100 vendors from both counties to determine which of their practices had effect on the bacteriological quality of the products. In addition, a total of 300 randomly selected members of the public in both counties were interviewed using questionnaires, to assess their attitudes, knowledge and perceptions concerning “doubles” consumption. Of a total of 196 samples each of “bara”, “channa”, condiments/spices and ready-to-eat “doubles” tested, the log₁₀ mean (±SD) total aerobic plate count (TAPC) per g was 4.87±5.51, 5.79±6.61, 6.26±6.77 and 6.88±7.91, respectively. The difference was statistically significant (P<0.05; χ²). Applying a recommended maximum standard of log₁₀ TAPC per g of 5.00, 10 (5.1%), 19 (9.7%), 57 (29.1%) and 78 (39.8%) of 196 samples of “bara”, “channa”, condiments/spices and ready-to-consume “doubles”, respectively, were deemed unfit for human consumption. Vendor practices, which significantly affected the prevalence of unfit “doubles” were re-use of leftover product (P=0.01), wearing of hand gloves (P=0.02), availability of water at sale outlet (P=0.0008) and source of water (P=0.0008). Consumption of “doubles” was more common amongst East Indians (69.2%) than other races (30.8%) (P<0.001) and amongst individuals who were aware that “doubles” can cause food-poisoning (61.4%) compared with individuals who did not have the awareness (36.0%) (P<0.03). Age, gender and occupational status of individuals did not significantly (P>0.05) affect consumption of “doubles”. The high prevalence of ready-to-consume “doubles” assessed unfit for human consumption coupled with a significantly higher proportion of consumers than non-consumers being aware that the product could cause food-poisoning, definitely poses a health risk to consumers of “doubles” in the population. Enforcement of sanitary practices during the preparation and sale of “doubles” should reduce the health risk.     

An Evaluation of Random Testing

Random testing of programs has usually (but not always) been viewed as a worst case of program testing. Testing strategies that take into account the program structure are generally preferred. Path testing is an often proposed ideal for structural testing. Path testing is treated here as an instance of partition testing, where by partition testing is meant any testing scheme which forces execution of at least one test case from each subset of a partition of the input domain. Simulation results are presented which suggest that random testing may often be more cost effective than partition testing schemes. Also, results of actual random testing experiments are presented which confirm the viability of random testing as a useful validation tool.